<p>For the electromagnetic drive asynchronous motorized spindle, there is an inevitable nonlinear coupling between its electrical and mechanical systems. However, few studies have focused on the nonlinear electromechanical coupling in motorized spindles. In this work, a fully analytical model is proposed to study the electromechanical coupling characteristics considering nonlinear vibration. The electrical model is established in the dq frame, and the mechanical model describing the coupling of bending and torsional vibration is developed. The electrical and mechanical models are solved iteratively in the time domain using the partition method. Electromagnetic torque and unbalanced magnetic pull constitute electromagnetic excitation and are derived. The mass eccentricity excitation from the attachment is deconstructed. The milling load with the time-varying delay is calculated. For bearings, considering their internal friction and nonlinear structure, the unbalanced load applied to the journal is calculated. In particular, the electromagnetic drive and energy conversion mechanisms are analyzed. The friction loss is considered to modify the electromagnetic torque. Experiments were carried out to measure vibration, force, and electrical signals to verify the proposed model. The vibration and stator current signature analysis is employed to investigate the&#xa0;electromechanical coupling. This work reveals the coupling mechanism between mechanical and electrical systems excited by nonlinear vibration. The results show that nonlinear electromechanical coupling can excite rich nonlinear behaviors such as frequency modulation and low-frequency pulsation.</p>